1. Field of the Invention
Chemical synthesis of 4-ketolutein is described. The synthesized compound is useful in the coloration of chicken egg yolks.
2. Description of the Related Art
Lutein is commercially produced in large quantities from marigold flowers (Tagetes erecta) for use as a food additive. Specifically it is used widely to color chicken egg yolks. However, while lutein imparts a strong yellow color to the yolk, it is desirable in many markets to add red coloration so that the resulting egg yolk is more orange in color. Typically this red coloration is obtained by the addition of paprika extract or canthaxanthin to the feed. Addition of these extracts to the feed significantly increases the expense. Thus, there is a need for a lutein product which can impart the desired coloration without subsequent addition of other colorants. If one could economically modify lutein itself to produce the desired orange-red coloration, there would be no need to add expensive extracts to achieve the desired effect. This, in fact, is the basis of our present invention.
Previously we have demonstrated a mild oxidative procedure for the conversion of zeaxanthin to astaxanthin (U.S. Pat. Nos. 5,973,211 and 6,329,557). We now have demonstrated a similar procedure for the conversion of lutein to 4-ketolutein in good yield. Mixtures of 4-ketolutein and lutein, which can be obtained by partial oxidation or by subsequent mixing of lutein with the 4-ketolutein obtained, demonstrate excellent coloration of egg yolks in trials.
Lutein is obtained in good purity by hydrolysis of the lutein esters extracted from Marigold flowers. It is semi-purified by several means and is sold for formulation into chicken feed where it imparts a yellow coloration to the egg yolk and also to the skin. However, chickens raised under native conditions generally consume other carotenoids which will impart some red coloration to the egg yolk. Therefore it is desirable to simulate this coloration through the use of mixtures of lutein with other carotenoids which possess reddish coloration.
The conversion of lutein to 4-ketolutein is shown in the following diagram:
